The present invention relates to an apparatus for dyeing textile substrates with a foamed dye. In one form, the present invention relates to an apparatus for dyeing textile substrates containing cellulosic fibers with a reduced leuco-state dye foamed with an inert gas and applied in the leuco foamed state in an inert atmosphere to the textile substrate and subsequently oxidized thereon to affix the indigo dye to the cellulosic fibers of the textile substrate. In another form, the present invention relates to dyeing a textile fabric substrate with foamed dye applied incrementally by a plurality of spaced applicators.
Dyeing cellulosic textile material, such as cotton yarn or fabric, with a leuco-state dye, such as indigo dye, has a large market, particularly for cotton denim clothing items, such as blue jeans. The fastness of the indigo dye on cotton and the deep color or shade that can be obtained make indigo dyed fabric a very popular product. However, dyeing cellulosic textile material with indigo dye is a complicated, complex and expensive procedure, because indigo in its natural state will not affix to cellulosic fibers. To render the indigo dye capable of affixing to cellulosic fibers, it is necessary to reduce the indigo by removing oxygen as by mixing with hydro (hydrosulfite) or other reducing agents to render the indigo a colorless leuco-state material. It then must be handled to remain in a substantially leuco-state until it is applied to the cellulosic textile material. To be capable of being applied, the leuco-state indigo dye must be sufficiently dilute to penetrate into the interstices of the cellulosic material. Typically, indigo dye is obtained from a supplier in a paste form that is, for example, in a 40% solution. It then must be further diluted to, for example, a 2% solution with a non-oxidizing liquid, such as hydro and caustic soda, to maintain the leuco-state to be capable of penetration into a traveling textile substrate that is immersed through a vat of the diluted indigo dye. Because of this dilution, it is necessary to pass the textile substrate through a series of sequential indigo dye vats with intermediate exposure to the atmosphere or other oxidizing agents to set the indigo applied during the preceding immersion. To obtain a desired deep color or shade, it is common to utilize a dyeing range having anywhere from four to eight, dye vats in series with arrangements of guide rolls between vats to assure proper oxidation of the indigo between vats. In addition, the dye in the vats must be continuously and rapidly recirculated in a tank or tanks into which reduced water or other similar material is added and regulated to remove oxygen taken up in the dye vats and to return any oxidized indigo dye to the reduced leuco-state.
A significant problem with prior art indigo dyeing ranges is that of waste dye and water disposal. Because of the numerous vats and the amount of dye liquor that must be provided, there is a significant quantity of dye liquor that must be disposed of at the end of every dyeing operation. This creates an undesirable substantial expense and environmental problem.
Another prior art dyeing system is disclosed in U.S. Pat. No. 4,613,335, issued Sep. 23, 1986, to Hans-Ulrich Berendt, et al. This patent discloses a process for dyeing or printing cellulosic-containing textile material with a reduced leuco-state dye in a foam carrier. While mentioning dyeing, the disclosure is primarily directed to printing, and there is no disclosure of the substrate being in a sealed, inert atmosphere. Rather, the substrate is exposed to the atmosphere as it approaches the applicator, as it passes across the applicator, and as it leaves the applicator. Therefore, there is no control of the condition of the substrate as it approaches and passes under the applicator and no control of the oxidation of the dye after it is applied to the substrate.
In contrast, the present invention, in one form, provides for the applicator face and substrate to be in a controlled inert atmosphere so that the foam can be applied without oxidation or controlled oxidation of the leuco-state dye and the foam can at least partially collapse in the inert atmosphere allowing the dye in its leuco-state to disperse on the substrate without oxidation or with controlled limited oxidation before it is fully oxidized as the substrate leaves the inert atmosphere, assuring that desirable affixing of the dye on the substrate occurs when the substrate is exposed to the atmosphere.
In another form of the present invention, the apparatus is not limited to dyeing of any particular textile fabric substrate, which dye can be in the leuco-state or any other form that is foamed for application to the traveling substrate. Also, it is not limited to a dyeing chamber sealed from ambient air, but can be utilized with a sealed chamber or a chamber that is open to ambient air. This form of the apparatus utilizes a plurality of spaced foam applicators applying dye in foam form onto the surface of the substrate in increments and being spaced apart to permit at least partial collapse of the foam between applicators.